Thermionic tube



wwms

Nov. 29, 1932. H.- w. PARKER THERMIONIC TUBE Filed March 15, 1952INVENTOR Hem-H MK Parker ATTORNEY Patented Nov. 29, 1932 UNH'lE s'rares1,889,,ltt

PATENT @FFFCE HENRY W. PARKER, OF TORONTO, ONTARIO, CANADA, ASSIGNOR TO,ROGERS RADIO TUBES, LIMITED, OF TORONTO, ONTARIO, CANADA, A CORPORATIONOF ONTARIO,

CANADA rnnnrrronrc TUBE Application filed March 15, 1932. Serial No.598,911.

My invention pertains to thermionic tubes and relates in particular tothermionic tubes employing screening electrodes.

One of the principal objects of my invention comprises producing athermionic tube of simplified form having screening electrodes.

A further object comprises producing an eflicient screen grid tube ofsimplified construction.

A still further object comprises producing a construction for screengrid tubes which, while retaining the same desirable electricalcharacteristics of such tubes now in use, may be fabricated in massproduction more easily and cheaply. v I

I accomplish the above desirable features and others which will behereinafter pointed out and discussed by extending the metallic memberwhich serves as the supporting medium for the active electron emissivesubstances of an indirectly heated cathode to form a shield for theterminal of the control grid and to function as a screening electrodefor cooperation with an inner screen electrode and outer screenelectrode which may be attached to the glass envelope of the tube toachieve fully effective screening.

In the drawing accompanying and forming a part of this specification andin which like reference numerals designate corresponding partsthroughout; 7

Fig. 1 is an elevation of my improved tube with a portion of the glassenvelope broken away;

Fig; 2 is a partially sectioned view of my improved cathode showing thedetails of the screening extension thereof.

Referring now particularly to the figures, my improved tube comprisesthe usual glass envelope 1 cemented in the usual base 27. A stem 26supports the usual anode 21 by means of standards 22 and 23, one ofwhich, 22, may serve as a terminal therefor. The. cathode 9 of theindirect heated type is provided with the usual heating wire 10, theterminals of which are connected as usual to the proper contactprongson" the bas'e '27. The heating wire 10 is maintained within thecathode cylinder 9 and out of electrical contact therewith by means ofthe cylinder 12 of refractory insulating material. The metallic cylinder9 of the cathode, preferably composed of nickel, is extended upwardbeyond the portion used as shown in'liig. 2 to carry the active electronemissive substances and is provided with a bushing 8 of refractoryinsulating material having a central aperture therethrough, throughwhich the terminal 6 of the control grid, supported by standards 18 and19, extends. The terminal 6 of the control grid is electricallyconnected with the usual terminal cap 5 secured to the top of envelope 1inthe usual manner. The terminal 6 emerges through an aperture in thewall of the cathode tube 9 and is prevented from contact therewith bymeans of a glass or ceramic bead 7. Electrical contact between thecontrol grid and terminal 6 is made through standard-19 as shown in Fig.l. The control grid is formed preferably of a helix of wire wound on thesupports 18 and 19.

The inner screen grid may be in the form of a metallic mesh but ispreferably formed of a helix of wire wound on supports 16 and 17. To thelower extremities of the screen grid supports 16 and 17 there isprovided a shouldered metallic ferrule 28 which is attached to supportspreferably by spot-welding. The shoulder of the ferrule supports awasher 29 of mica or other refractory insulating material provided withapertures through which the standards 18 and 19 of the conrto-l gridpass and also an aperture through which the cathode 9 passesand servesas a. means for maintaining the relative positions of the control grid,screen grid and cathode. The upper extremities of the standards of thecontrol grid 18 and 19, the cathode 9 and the upper extremities of thescreen grid supports 16 and 17 pass through a washer "of mica or otherrefractory insulating ma terial 15 which serves to maintain the relativepositlons of the cathode, control grid and screen grid. The entireassembly of the inner screen grid, control grid and cathode justdescribed is spot-welded tosupports orstandards l3 and 14 held in thepress 26. One of these standards, as 14, may serve as the terminal forthe inner screen grid.

The outer screen 20 may, of course, be placed inside the envelope 1adjacent the outer surface of the anode, but preferably consists of ametal such as zinc, sprayed or otherwise applied on the outer surface ofthe envelope 1 and covering practically the entire outer surface of theenvelope exposed above the base except for a portion of the top wheresufiicient space is left to provide the necessary insulation resistancebetween the control grid cap 5 and the metallic coating 20. Thismetallic coating serves as the outer screen grid usually placed withinthe envelope 1 and adjacent the anode 20. This outer screen may be, ifdesired, connected by means of a conductor within the base 27 to thecathode prong which is connected to the cathode cylinder by means of thecontact terminal 11, although such connection is not necessary as thecoating 20 may be connected to ground in other obvious ways.

In mass production utilizing automatic exhaust machines, it is desirableto provide a slot or opening 25 in the anode 21 and to bridge this slotby a wire conductor 24 in the form of a hair-pin the extremities ofwhich are preferably spot-welded to the anode in the position shown inFig. 1 to allow the radio frequency currents used in heating up theelectrodes of the tube in the exhaust process to quickly as possiblepenetrate to the inner grids that these elements of the tube may bereadily heated to redness during the "exhaust process. The hair-pinconductor 24 acts as the high resistance bridge across the gap in theanode and reduces the heat of the anode sufficiently to allow the gridswithin the anode to quickly reach the desired temperature without undulyheating the anode.

Screen grid tubes now in use employ invariably an inner screen betweenthe control grid and the anode and an outer screen ad- 1' acent theanode but within the glass envelope of the tube and both of thesescreens are electrically united with a top screen or cover entirelycovering the top of the anode in order that the control grid lead orterminal may be shielded.

I have found by experiment that my improved construction, whereby thecontrol grid 7 lead is shielded through being maintained in an extensionof the metallic cathode tube, produces exactly the same degree ofshielding as the usual type hereinbefore referred to and at the sametime evidences the same desirable low capacitance between the controlgrid and the anode as that in the usual tube and that, further, theelectrical characteristics are in all other respects practicallyidentical,

It will be obvious that as the inner screen grid, control'grid andcathode may be con structed in the form of a sub-assembly and introducedas such in the final assembly in the press by merely spot-welding tothe-standards provided therefor in the press, that the construction inmass production is greatly simplified and consequently cheapened.

It will be further obvious that all electrodes in the sub-assembly maybe definitely fixed with respect to their relation to each actly thesame manner as the top anode 1 screens now used and that my constructionthus simplifies the construction of screen grid tubes as nowmanufactured through the elimination of the upper or top cover screen towhich the usual inner and outer screen grids Q are connected. Mysimplified construction, therefore, while producing a tube which may bemore easily and cheaply constructed in mass production performs exactlysimilar to tubes of the same general type now in use.

Having thus completely described my invention, what I claim as new anddesire to secure by Letters Patent of the United States 1s:

1. An electrode assembly for thermionic tubes comprising, a cathode inthe form of a metallic cylinder, electron emissive substances on aportion of the exterior thereof, a heating element within said cylinder,a control grid without said cylinder, a terminal for said control gridinsulatingly maintained within a portion of said cylinder and means formaintaining the relative positions of said cathode and said controlgrid.

2. An electrode assembly for thermionic tubescomprising a cathode in theform of a metallic cylinder, electron emissive substances on a portionof the exterior thereof, a heating element within said cylinder, acontrol grid without said cylinder, a terminal for said control gridinsulatingly maintained within a portion of said cylinder and a screengrid and anode operatively associated with said control grid andcathode.

3. An electrode assembly for thermionic tubes comprising, a cathode inthe form of a hollow metallic member, electron emissive substances on aportion of the exterior thereof, a heating element within said memberadjacent the portion coated with electron emissive substances, a controlgrid adjacent said member, a terminal for said control grid passingthrough the wall of said member and insulatingly maintained within aportion of the interior of said member and means for a:

maintaining the relative positions of said cathode and said controlgrid.

4. An electrode assembly for thermionic tubes comprising, a cathode inthe form of a hollow metallic member, electron emissive substances on aportion of the exterior thereof, a heating element within said member,and adjacent the portion coated with electron emissive substances, acontrol grid adjacent said member, a terminal for said control gridinsulatingly maintained Within the interior of a portion of said memberand a screen grid and anode operatively associated with said controlgrid and cathode.

5. A thermionic tube comprising, an enclosing envelope, a press withinsaid envelope, a screen grid supported by said press, a control grid, acathode comprising a hollow metallic member, a portion of the exteriorsurface of which is coated with electron emissive substances, a heatingelement within said member and adjacent said coated portion, an aperturein the wall of said mem-' ber intermediate the extremities thereof and aconductor connected to said control grid and insulatingly maintained insaid aperture and extending through a portion of the interior of saidmember, and an anode adjacent said screen grid and supported in saidpress.

6. A thermionic tube comprising, an enclosing envelope, a press withinsaid envelope, an anode supported by said press, a screen grid withinsaid anode and supported by said press, a control grid within saidscreen grid, a cathode comprising a metallic cylinder, a portion ofwhich is coated with electron emissive substances and a heater thereforwithin said control grid, a connection for said control grid passinginsulatingly through the wall of said metallic cylinder and insulatinglyextending through a portion of the interior thereof and a contactsecured to said envelope and connected to said connection for saidcontrol grid.

7 A thermionic tube comprising, an enclosing envelope, a press withinsaid envelope, a screen grid supported by said press, a control grid, acathode comprising a hollow metallic member, a portion :of the exteriorsurface of which is coated with electron emissive substances, aheatingelement within said member and adjacent said coated portion, an aperturein the wall ofsaid member intermediate the extremities thereof, aconductor connected with said control grid and insulatingly maintainedwithin said aperture and extending through a portion of the exterior ofsaid member, an anode adjacent said screen grid and supported by saidpress and an additional screen grid electrode provided upon the exteriorsurface of said enclosing envelope for cooperation with said cathodemember and said firstmentioned screen grid.

HENRY WPPARKER.

